7.22am: Japan has been rocked by a series of earthquakes causing a major Tsunami. Here's some details from our Japan correspondent, Justin McCurry:

A series of powerful earthquakes struck north-east Japan on Friday afternoon, triggering warnings of tsunami as high as 10 metres and shaking buildings in Tokyo.

The first earthquake struck at 2:46pm local time and measured magnitude-8.8, according to the US geological survey. Within 30 minutes the same region was rocked by two more big quakes of slightly lower intensity, Japanese news reports said.

The first quake, Japan's biggest for seven years, struck at a depth of six miles about 80 miles of the eastern coast, according to Japan's meteorological agency.

The Pacific tsunami warning centre in Hawaii said a tsunami warning was in effect for Japan, Russia, Marcus Island and the Northern Marianas. A tsunami watch has been issued for Guam, Taiwan, the Philippines, Indonesia and Hawaii.

All flights in Japan were grounded immediately after the quake while officials checked for runway damage. Strong tremors were felt in Tokyo about 30 minutes after the quake. Newsreaders in the capital wore helmets as they gave updates, while office workers rushed out of buildings on to the street.

Television showed a building on fire in the Odaiba district of Tokyo, although it was not immediately clear if the blaze was connected to the earthquake.

Other footage showed water levels rising quickly in the coastal town of Miyako in Iwate prefecture on Japan's north-east Pacific coast. Public broadcaster NHK showed cars, trucks, houses and buildings being swept away by tsunami in Onahama city in Fukushima prefecture.

TV news presenters repeatedly warned people on the Pacific coast to head for higher ground.

•Eight military planes scrambled to survey damage. Prime Minister Naoto Kan asks people to remain calm and orders the military to do their utmost to act. Cabinet to meet.

•The government says more tsunami possible.

• Central bank vows to do utmost to ensure financial market stability

•Several nuclear power plants shut down automatically. Tepco's Fukushimi No. 1 plant had an equipment problem after the quake, but safety is ensured, officials say. At least one nuclear power station operating normally. Oil refineries have shut down and a major steel plant was ablaze.

8.30am: This video shows the extent of the tidal wave in Sendai, as well as footage of a huge fire raging:

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8.34am: The UN says 30 international search and rescue teams are on alert, ready to help Japan deal with the disaster.

Tsunami alerts have been extended to the following countries among others:

9.11am: The International Federation of Red Cross and Red Crescent Societies is warning that the tsunami triggered by the earthquake is currently higher than some Pacific islands which it could wash over. Paul Conneally, spokesman for the federation, the world's biggest disaster relief network, told Reuters in Geneva:

Our biggest concern is the Asia and Pacific region, where developing countries are far more vulnerable to this type of unfolding disaster. The tsunami is a major threat. At the moment, it is higher than some islands and could go right over them.

9.13am: Media reports in Japan are suggesting the death toll has risen to 19, according to the BBC.

It's kind of crazy because restaurants and convenience stores have remained open despite there being no power. In the background you can hear sirens. People are still going to restaurants and getting food at convenience stores...

The city seems to be in pretty good shape. There's no damage, no buildings crumbling that I've seen. As I said some people are still eating in restaurants, even though it's pitch black. There's no power so I expect people are just trying to get back to normal.

Just had two earthquakes off the southern coast. Lot of stuff fell over. Got knocked down going down stairs& bumped my head. More to come

@oculardisaster all trains and busses stopped, power and comma were down for a bit, think I hit my head but otherwise good

9.53am: Some worrying news regarding one of Japan's nuclear plants from Justin McCurry:

According to Kyodo news, the operator of the Fukushima No. 1 nuclear plant in northeast Japan has reported an abnormality after today's earthquake, the industry ministry said. The system to cool reactor cores in case of emergency stopped at the No. 1 and No. 2 reactors of the plant, which is run by Tokyo Electric Power, Kyodo quoted the ministry as saying.

9.57am: The Tsunami watch issued for the entire western coast of the United States and Canada from the Mexican border to Chignik Bay in Alaska (see 9.24am) has now been upgraded to a tsunami warning. That means there is an imminent threat of a tsunami.

10.02am:Kyodo News is reporting that a fire has broken out in a turbine building at Onagawa nuclear power plant in Miyagi prefecture in the wake of today's earthquake.

10.04am: Natural gas storage tanks are alight at the Cosmo oil refinery in Ichihara near Tokyo, with huge flames reaching into the sky.

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10.07am: BBC is now reporting the death toll has risen to 26.

Photograph: PA Wire/PA

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10.18am: The UK foreign secretary, William Hague, said the UK has offered assistance to Japan:

My thoughts are with the people of Japan at this time. We are in contact with the Japanese government and I have asked our Ambassador in Tokyo to offer all assistance we can as Japan responds to this terrible disaster...

We have set up a crisis centre in the Foreign Office to co-ordinate our response and offer advice to anyone concerned about relatives or friends in Japan. We are not aware of any British casualties at this time...

Following tsunami warnings across the region our embassies and consulates are preparing to provide assistance. Rapid deployment teams are ready to travel immediately to the areas of most need.

10.31am: My colleague, Simon Tisdall, has some information on Sendai, the city closest to the earthquake.

Sendai, the city closest to the epicentre of the earthquake, has a population of about one million people. The Miyagi prefecture, of which Sendai is the capital, and neighbouring Fukushima prefecture, to the north of Tokyo, are predominantly rural and agricultural areas, with few major populations centres.

The Tohoku region is marked by the Ou volcanic mountain range that runs north to south. It is known historically as the granary of Japan due to its production of rice and other farm produce. Much of the population lives away from the coast, in the inland lowland areas.

Tohuku is famed for its scenery and harsh climate and is a popular tourist destination.Based on the most recent census, Tohoku's population is 9.63 million, about 7% of the population of Japan. The land is mountainous and volcanic. In recent years, smaller towns in Tohoku have seen population decreases as young people move to the big cities further south.

The level of post-war development was dramatically lower than in Japan's Pacific belt (the urban zone running from Kanto through Osaka to Fukuoka.). Tohoku remains relatively poor.

10.34am: Authorities are now saying at least 32 people have been killed, AP reports.

10.41am: CNN Chile reports that the waves are due to hit Chile this afternoon, with the first impact arriving at Easter Island at 5.55pm local time (3.55pm GMT).

10.42am: Dr Roger Musson, an earthquakes expert at the British Geological Survey, tells the BBC this is the sixth largest earthquake it has recorded [since 1900]. Compared to the Christchurch earthquake in New Zealand, "this earthquake is thousands of times bigger, this is really huge". Aftershocks will continue for weeks, he predicts.

10.47am: Russian authorities on Friday evacuated some 11,000 residents from coastal areas on Pacific islands before they were hit by tsunami waves unleashed by a magnitude 8.9 earthquake off Japan's northeastern coast, AP reports.

The regional emergency officials said that the waves reached several towns and villages on the Kurils, four Pacific islands that the Soviet Union seized from Japan in the final days of the World War II, but caused no damage. The islands lie as close as six miles (10km) from Japan's Hokkaido island.

A 3m wave reached the village of Malokurilskoye and some other villages recorded lower water levels, the Russian emergency situations ministry said. There were no immediate reports of damage.

Authorities on the Kamchatka Peninsula further north had also expected to be hit by the tsunami but said it didn't reach the area. The ITAR-Tass news agency quoted seismic expert Pyotr Shebalin as saying that there is a strong likelihood that the Japanese quake could trigger powerful quakes on Kamchatka or the Kurils over the next nine months.

Photograph: Anthony Devlin/PA

10.50am: My colleague Nick Watt, who has just been listening to the prime minister, reports that Britain is looking at providing aid to Japan.

David Cameron offered Britain's condolences to the people of Japan as he arrived at the emergency EU summit in Brussels this morning. The prime minister said: "We send our sympathies and condolences to the Japanese people. We've had a terrible reminder of the destructive power of nature and everyone should be thinking of that country and its people and I've asked immediately that our government should look at what we can do to help.''Jose Manuel Barroso, the president of the European Commission, and Herman Van Rompuy, the president of the European Council, will issue a joint statement on Japan at lunchtime.

10.52am: Here's a video of Japanese MPs in parliament when the quake struck:

10.56am: The number for the UK foreign office helpline for individuals in the UK concerned about the safety of friends and relatives in Japan is 020 7008 0000.

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11.03am: We've been getting some vivid accounts of the earthquake from people in Japan in the comments section. Here are just a couple.@antshu

I live in Tokyo and have done for some years. Without doubt this is the worst earthquake I've experienced.The building I was in was shaking badly, it was very scary. I managed to get a taxi back home as all the trains have stopped. Thankfully my family is OK.I am very concerned though for my (Japanese) wife's parents. They live in Miyagi which is the epicentre. We are unable to call as all the phone networks are down. The pictures on Japanese TV look horrendous with enormous tsunamis crashing into the coast.

I just spent two hours hiding in the hills above my coastal village. I live in the south but we still got hit by a 1.5 metre wave. I'm concerned it may trigger a massive earthquake in the south that happens once every 100-150 years. The scenes from northern Japan are very saddening... it looks exactly the same as where I live. My thoughts are with them but Japan is well prepared for such events so hopefully things aren't as bad as they could have been.

11.12am: Journalists at the Japan Times are soldiering on with covering the tragic events, while all the time having to be alert in case they need to evacuate:

11.20am: An idea of the level of aftershocks being experienced in Japan can be gauged from the fact that the US geological survey is currently listing 40 earthquakes in Japan today.

11.22am:Japan has declared a "nuclear emergency" as attempts to cool reactor at northern plant are 'not going as planned', NHK is reporting.

11.31am: The Associated Press has more details on the state of emergency issued at nuclear plant after its cooling system failed:

Chief cabinet secretary Yukio Edano says the nuclear power plant in Fukushima developed a mechanical failure in the system needed to cool the reactor after it was shut down in Friday's earthquake.

He said the measure was a precaution and there was no radiation leak at the Fukushima No. 1 power plant. He said the facility was not in immediate danger.

11.36am: My colleague, Barry Neild, has been speaking to Colin Taylor, a professor of earthquake engineering at Bristol University. Taylor said Japan is a world-leader in quake-resistant construction, but the size of Friday's earthquake would test even its strongest buildings, none of which are tsunami-proof.

The Japanese, the Americans and the New Zealanders have led earthquake design for the past few decades. Their constructions are quite robust, and go a long way to minimising the damage from the earthquake, but you can never make anything totally earthquake-proof. From an earthquake this big there is bound to be significant damage, but the main problem is the tsunami. There's very little you can do to protect buildings from a tsunami. The energy from the wave is too much for them to withstand. It comes ashore at 40-50 miles per hour and has huge momentum, which is virtually impossible to design against.

The Ginza line of the Tokyo Metro is working again. The rest [of the network] is still down and many people can't get home

11.49am: Some very worrying news comes via the Kyodo news agency, which is reporting that a ship carrying 100 people was swept away by the tsunami.

12.02am:@usasoneiaswe, in the comments section, details people trying to get on with their normal lives, amid vivid signs of what has occurred, which tallies with the account given by Tristen Mathers (see 9.41am):

Pretty weird, just been to get some err, 'supplies' from the supermarket, everyone going about their shopping --as the Japanese are apt to do-- while skirting round produce strewn hither and tither and then walking back I noticed that every single bicycle, of which there are a lot, was on the floor. A sea of scattered frames and rotating wheels.

12.03pm: Japanese police say the death toll from the earthquake now stands at 40, with 39 missing, AP reports.

12.18pm: The US president Barack Obama said in a statement:

Photograph: Chris Carlson/AP

We will continue to closely monitor tsunamis around Japan and the Pacific going forward and we are asking all our citizens in the affected region to listen to their state and local officials.

Meanwhile his home state of Hawaii has ordered evacuations of coastal areas.

AP reports that the main airports on at least three of the major islands - Maui, Kauai and the Big Island of Hawaii - were shut down as a precaution, and the US Navy ordered all warships in Pearl Harbor to remain in port to support rescue missions as needed.

Authorities also ordered evacuations from low-lying areas on the US island territory of Guam in the western Pacific, where residents were urged to move at least 50 feet (15 meters) above sea level and 100 feet (30 metres) inland. Guam initially appeared to have emerged unscathed, according to AP.

12.30pm: A fire at the Onagawa nuclear plant has been extinguished, according to the International Atomic Energy Agency. Note: this is not the plant in respect of which a state of emergency was issued because of problems with its cooling system.

12.39pm: A train is unaccounted for in the coastal areas affected by the Tsunami, Reuters is reporting.

1.41pm: We're just back online after a bit of a technical problem.

The UK's international development department, DFID, is monitoring the spread of the tsunami across the Pacific. It says Japan is not requesting foreign assistance and has asked overseas aid teams to remain in their own countries at present.

Any UK government aid is more likely to be directed at islands or states other than Japan. British search and rescue teams are on an initial level of alert, gathering their equipment and preparing themselves but not yet heading for the airport.

Associated Press is reporting that the tsunami reached Hawaii shortly after 1pm UK time. No reports of damage yet.

1.47pm:Japan police say 200 to 300 bodies have been found drowned in Sendai.

1.51pm: Here's a quick recap of events so far today:

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•An earthquake measured at 8.9 magnitude by the US Geological Survey, the sixth biggest since 1900, struck Japan today. The USGS has recorded more than 50 subsequent earthquakes.

•The earthquake triggered a tsunami with 10m-high waves hitting the northern port of Sendai. Waves have swept across farmland, sweeping away homes, crops, vehicles, triggering fires. Tsunami warnings and watches have been issued in dozens of other countries.

•The death toll has been rising throughout the morning. The death toll has been rising throughout the morning. Police said at least 60 people have been killed and 56 are missing.. But there are fears many more could be dead and police have just said 200 to 300 drowned bodies have been found in Sendai. A ship carrying 100 people was swept away by the tsunami, according to the Kyodo news agency. Reuters is reporting that a train is unaccounted for in coastal areas affected by the tsunami.

•A state of emergency has been declared at a nuclear plant in Fukushima. The government said it was a precaution due to a mechanical failure in the system needed to cool the reactor after it was shut down. The authorities said there was no radiation leak but people within 2km of the plant have reportedly been told to evacuate their homes.

•The Japanese prime minister Naoto Kan urged people to help their neighbours and to act to "minimise the damage". "We ask the people of Japan to exercise the spirit of fraternity, help each other and act fast," he said.

1.53pm: Police have reported a major explosion at a petrochemical complex in Sendai, the BBC is reporting.

The Pacific Tsunami Warning CentrE said Kauai was the first island hit early Friday by the tsunami. Water rushed ashore in Honolulu, swamping the beach in Waikiki and surging over the break wall in the world-famous resort but stopping short of the area's high-rise hotels.Waves at least 3ft (a metre) high were recorded on Oahu and Kauai, and officials warned that the waves would continue and could become larger.

Roadways and beaches were empty as the tsunamis struck the state, which had hours to prepare. Residents in coastal areas of Hawaii were sent to refuge areas at community centers and schools while tourists in Waikiki were moved to higher floors of their high-rise hotels. People waited in long lines stocking up on gas, bottled water, canned food and generators, and officials told residents to stock up on water and fill their cars with gas.

Waves are predicted to hit the western coast of the United States between 11am and 11.30am EST (4pm to 4.30 GMT) today.

2.13pm: Here's another picture which brings home the horror of what has hit Sendai. At first glance the planes and cars look almost like toys.

Light planes and vehicles swept from Sendai airport in northern Japan sit among the debris from the tsumani. Photograph: AP

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2.18pm: The UN secretary general Ban Ki Moon has said the UN will do "all it can to mobilise humanitarian assistance".

2.30pm: A Japanese coast guard official says a search is under way for a ship carrying 80 dock workers that was swept away when a tsunami struck the northeastern coast, AP reports.The vessel was washed away from a shipbuilding site in Miyagi prefecture.

I was walking down a set of big stone steps while they wobbled underneath me. You have got these concrete buildings and it's as if they are made of jelly. It's in your mind that the building could collapse at any moment. Friends who were in skyscrapers said being on higher floors was terrifying because they were swaying so much.

Opposite the station itself they are building a new skyscraper, already maybe 40 storeys high, with two huge construction cranes on top. It was shaking and swaying from left to right with the cranes swaying.

2.37pm: My colleague Barry Neild has been speaking to Richard Gordon, director of Bournemouth University Disaster Management Center, who described the disaster as "like Hurricane Katrina and the Haiti earthquake rolled into one":

One of the key things is that there is going to require a lot of work on casualty tracking since many families will have been divided. People are now making hundreds of telephone calls to find out if members of their family are alive. The mobile phone network will be at capacity and it will be interesting to see if it can handle the pressure or will invoke procedures limiting access to public calls to emergency services. The quake struck at around 2pm in Japan, which means schools will have been still working, so many people evacuating will have the added stress of trying to reach their children. Hospitals are also going to be overwhelmed. It is a major humanitarian disaster -- like Hurricane Katrina and the Haiti earthquake rolled into one.

2.45pm: Some updates from Reuters on the situation in Japan:

- A large waterfront area near Sendai city is on fire, TV reports say. - One train is derailed and another missing in Miyagi prefecture, Kyodo says. - Tokyo's Narita international airport has resumed some outbound flights after earlier closing, halting flights and evacuating passengers. - Television reports a major fire at Cosmo Oil Co's Chiba refinery east of Tokyo, and a fire was reported at JFE's steel plant, also in Chiba.

2.57pm: Thank you to everyone sharing their accounts of the earthquake in the comments section. Sorry we can't highlight each one individually. Here are a couple more eyewitness accounts from Tokyo, passed on by my colleague, Dale Berning:

This was definitely the strongest earthquake we've both ever experienced. We are still feeling tremors now, small ones, but at their worst, the tremors felt like they would never end. We took shelter in a bookshop nearby. When we went outside these huge Tokyo buildings were swaying from side to side, it was scary. But Tokyo hasn't seen much damage. There aren't broken buildings or anything, and we have electricity – just some things which have fallen off shelves etc. The big problem is that the JR trainlines are down and all the businessmen and women who commute into town from outside can't get home.

We are back at home now, and outside the streets are full of people just walking. They don't have anywhere to stay for the night – the hotels etc are all full, so people have just started walking. But a lot of people can't just walk home. Our friend Masuda lives in Yokohama, his wife works in Tokyo – it would take her over 10 hours to walk home so she can't get home, she has to stay at her office tonight.

We have family – Daisuke's uncle – in Sendai, but we haven't been able to reach them. All the networks and phone lines are down. We are hoping to hear from him soon. The thing is, in Sendai/Miyagi, earthquakes are really frequent so generally people know what to do.

Yasuko Kaneko works in an art gallery in Roppongi, Tokyo

The earthquake was strong and long. It might be the biggest one I have ever had.We hold the art works exhibited, but it was quite long, so my boss suggested to leave the works and run out.But Tokyo is not in the panic condition.There are traffic jams, but so many people are walking through the town. If I didn't know about the earthquake, I would think it was a festival or something. But of course, many things are strange. There is little food on the shelves in the convenience stores like Family Mart. Some trains are restarting, but they are not busy... We cannot use mobile and SMS. Skype and twitter were really helpful for knowing what the situation is.

3.06pm: The Guardian's US environment correspondent, Suzanne Goldenberg, has sent in an update from the US

Craig Fugate, the head of the federal emergency management agency (Fema), said Guam is now in the clear but he warned residents of Hawaii it is too early to assume they are in the clear and the tsunami has passed. He told MSNBC:

It is still developing. We still haven't seen the full effects in the Hawaiian Islands. This can actually take several hours for this energy and the water to move through. People should not drop their guard until they hear from their local officials that they have got an all-clear.

3.12pm: Some more information from the US where residents in parts of northern California have evacuated their homes in anticipation of the tsunami, AP reports. Authorities in Oregon have also advised coastal residents to evacuate and schools were to be closed along the coast.

From AP:

"There are some evacuations going on in Del Norte and San Mateo," counties, said Jordan Scott, a spokesman for the California Emergency Management Agency.

Del Norte is the northernmost California coastal county, while San Mateo is the county just south of San Francisco that includes much of Silicon Valley. However, the technology centre is well inland.

Canada has issued tsunami advisories for parts of British Columbia on the coast.

3.24pm: Television pictures show a huge fire raging in Kesennumma, in Miyagi prefecture, the area worst affected in Japan. It looks as though the whole city is on fire.

BBC screengrab guardian.co.uk

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3.34pm: The death toll has reached three figures, according to Japanese police. Their numbers do not include the 200 to 300 said to have been found in Sendai. The latest police figures put the number killed at 110 with 350 people missing and 544 injured.

3.42pm: Here's some frightening footage of the huge fire raging in Kesennumma.

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3.48pm GMT: The first waves from the tsunami have now reached the US mainland along the northern California coast and southwestern Oregon. The Oregon coast is expected to be the worst affected, with surges of six to eight feet (about two metres) expected.

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This is Richard Adams in the Guardian's Washington bureau taking over live blogging.

3.52pm GMT: Good news regarding the fate of Japan's nuclear reactors: the World Nuclear Association says it understands the cooling problems at the damaged Fukushima plant are "under control".

3.56pm GMT: There are very disturbing reports of a dam breaking in Japan's Fukushima prefecture, washing away homes – and of course it is also close to the nuclear reactor mentioned below.

4.01pm GMT: While attention naturally focuses on the devastation in Japan, the low-lying Pacific islands in the path of the tsunami are at risk.

We remain worried about the impact waves may have on small island states such as Tuvalu or Samoa. We have several teams and partner organisations in region that are following the situation on the ground. Given these states are low lying and populations are spread out over many islands, even relatively small waves have the potential to be very damaging and complicate any humanitarian response.

It seems that the tsunami has not affected the Philippines and Indonesia for the moment, although they may still be hit by second and third waves soon. Oxfam is in a position to respond in these countries if required.

4.05pm GMT: In Guam, the force of the tsunami broke two US Navy submarines from their moorings, but tug boats corralled the subs and brought them back.

I've just got home after walking across Tokyo for six hours (all the trains were down, so that was the fastest way). The streets were very busy, as you would expect, but there was very little visible damage. I passed one building with a lot of fire engines and ambulances (Kudan Kaikan), and when I got home I heard that there had been a fatality there, and there was an area where some tiles had fallen onto the street, but otherwise the damage seemed to be limited to things falling off shelves. There were more ambulances and fire engines out than normal, of course, but I also passed fire stations with fire engines and ambulances in the station, with the staff standing around, obviously ready to go on a moment's notice, but equally obviously not currently required. The other ten million people walking home seemed fairly calm, most likely because they could see the same lack of damage as I could.

4.10pm GMT: The US has sent emergency supplies of coolant to a Japanese nuclear plant affected by the massive earthquake, Hillary Clinton has revealed.

"We just had our Air Force assets in Japan transport some really important coolant to one of the nuclear plants," the US secretary of state said in Washington DC.

"Japan is very reliant on nuclear power and they have very high engineering standards but one of their plants came under a lot of stress with the earthquake and didn't have enough coolant."

4.16pm GMT: Mathew Honan is a resident of Ocean Beach in San Francisco, where the tsunami is expected to hit shortly. He has set up a live webcam with a view of the beach which you can see here.